1. Field of the Invention
This invention relates in general to the field of oil well drilling rig equipment. In particular, the invention relates to power equipment for spinning drill pipe.
2. Description of the Prior Art
During the making up or breaking out of joints between stands of drill pipe, one stand is held stationary by a back-up tong, while the other stand is rotated. A torque wrench is used for final make-up and for initial break-out. During initial make-up or final break-out, a different tool is used to spin the drill pipe at a high speed.
The cheapest way to spin drill pipe is with a spinning chain. However, spinning chains are dangerous and are not as effective on heavier pipe and drill collars.
Hydraulically powered drill pipe spinners were developed to replace spinning chains. Power drill pipe spinners typically have two pairs of opposed rollers. One roller of each pair is power driven, and the other applies pressure to the drill pipe to keep the pipe against the driven rollers.
The pressure rollers are typically pivotable, to allow entry of the drill pipe into the body of the spinner. One method of pivoting the pressure rollers is to mount the pressure rollers on pressure arms, which are pivotable about one or two pivot pins. One or two hydraulic cylinders are used to apply force to the pressure arms.
It is desirable to multiply the force of the cylinders, particularly after the pressure rollers contact the drill pipe. Force multiplication allows a smaller hydraulic cylinder to maintain sufficient pressure on the drill pipe to avoid slippage.